Impact resistant clear sheets for applications such as aircraft windows and bullet-resistant security panels are often formed by laminating or co-joining vinyl (acrylic) sheet, polycarbonate and glass layers with polyurethane or polyvinyl butyral (“PVB”) interlayers, such as by a heat-lamination process using urethane film for bonding.
Polyvinyl (polyacrylic) sheets are easily formed by cell casting from relatively non-hazardous and inexpensive materials. Problematically, polyvinyl is brittle and the formed sheets must be very thick or laminated with other materials (e.g., polycarbonate or polyurethane) in order to provide impact resistance sufficient to stop projectiles such as high-powered hand gun rounds.
Polyurethane cast sheets provide superior impact resistance properties as compared to polyvinyl. Problematically, as compared to polyvinyl, polyurethane cast sheet is made from more expensive raw materials and frequently involves the use of hazardous chemicals. Moreover, cast polyurethane is difficult to produce due, in part, to very high viscosity of the starting materials which often must be maintained at high temperatures so that they can be poured, difficulty with short pot life, and difficulties in releasing cast polyurethane from the casting surface.
There is a need in the art for polymeric material that can be easily cast as sheets, can be prepared from relatively non-toxic material, and that exhibits superior bullet and impact resistance, clarity, and low haze.